Contact structure for mercury relays



Nov. 24, 1959 A. J. KODA CONTACT STRUCTURE FOR MERCURY RELAYS Filed Jan.23, 1958 INVENTOR. 742 77-02 J K904 BY ATTQzA/E/s.

United States Patent 01 CONTACT STRUCTURE FOR MERCURY RELAYS Arthur J.Koda, Morton Grove, Ill., assignor, by mesne assignments, to C. P. Clare& Company, Chicago, 111., a corporation of Delaware Application January23, 1958, Serial No. 710,816

4 Claims. (Cl. 200-112) This invention relates to a relay constructionand, more particularly, to an improved contact element for use inmercury contact switches.

The improved operating characteristics of mercury contact switches suchas high operating speeds, lack of contact bounce, and low contactresistance with small contact pressure, have led to the increased use ofthese types of switches in many diflerent applications. In some types ofapparatus, such as computing equipment, the high speed of operation ofthe mercury switch has made it a useful computer component because ofthe high speeds at which computing operations are performed. However, inthe high speed operating conditions normally encountered in computingoperations, a bridging of the contacts which has been observed to occurat random intervals adversely affects the reliability of these switchesas computer components. In the bridging phenomena, the make and breakcontacts of the switch, which are alternately engaged by a movablearmature, are shorted.

A study of the operations of the mercury contact switches with highspeed photographic equipment indi- -trol of an applied magnetic field.

cates that, during the operation of the relays, thedeflecparticular, inthe fillets formed between the contact elet ments and the terminal pins.When the mass of mercury contained in the globules becomes great enoughto be displaced by gravity or vibration, for instance, these globulesmove toward the upper end of the armature and the contact elements toform a coherent mass of mercury electrically bridging the oscillatingarmature and the make and break contact elements. This avalanche effectis of variable duration and occurs at random intervals. However, it hasbeen observed to persist for periods of up to two hundred and fiftymilliseconds at intervals having a median recurrence of around fourhours. In the speeds normally used in the operation of computingapparatus, a short circuit of this duration and this frequency ofrepetition cannot be tolerated because of the adverse effects on theaccuracy of the apparatus.

Accordingly, one object. of the present invention is to provide a newand improved contact element for a mercury contact switch which obviatesthe avalanche effect. i

Another object is to provide an improved terminal pin and contactelement assembly for a mercury contact switch in which the upper andlower end surfaces of the contact element are tapered towards thearmature to prevent the accumulation of globules of mercury in thefillets between the contact elements and the terminal pins. A stillfurther object is to provide a terminal pin and contact element assemblyfor use in mercury contact switches in which a contact element carriedon a terminal pin is provided with inclined end surfaces, both of whichare inclined toward a horizontal plane passing through the contactelement to intersect this plane at an angle of 45 or less.

In accordance with these and many other objects, an embodiment of thepresent invention comprises a generally vertically extending glassenvelope in the lower end of which is sealed a common terminal having anupwardly capillary type armature which is oscillated between twodisplaced or extreme positions under the con- In the upper end of theglass envelope are provided two pairs of spaced and depending terminalpins, each carrying a contact element. The upper end of the armature isdisposed between the two pairs of pins and is normally biased bysuitable means to engage the contact elements carried on the pair ofbreak terminal pins. Thus, when the armature is subjected to analternating magnetic field,

the upper end of the armature alternately moves intoand out ofengagement with the two contact elements on the make terminal pins andthe two contact elements on the pair of break terminal pins.

The lower end of the sealed envelope is provided with a reservoir ofmercury which moves upwardly along the armature to the upper end thereofby capillary action. Thus, when the armature is deflected between themake and break positions, the mercury on the upper end of the armaturewets the contact elements and, in part at least, is transferred to theadjacent surfaces of the terminal pins and the contact elements to formglobules. In accordance with the present invention, the upper and lowerend surfaces of the four contact elements are beveled or taperedinwardly toward the interposed upper end of the armature so that themercury cannot collect in the fillets between the terminal pins and thecontact elements. By avoiding the accumulation of an excessively largeamount of mercury in these fillets and on the terminal pins immediatelyadjacent the contact elements, it has been determined that the avalancheetfect is prevented so that the contacts are not bridged by a large massof mercury.

Many other objects and advantages of the present invention will becomeapparent from a consideration of the following detailed description whentaken in conjunction with the drawings wherein:

Fig. 1 is a sectional view of a mercury contact switch including theimproved terminal pin and contact element assembly of the presentinvention;

Fig. 2 is an enlarged sectional view taken along line 22 in Fig. 1assuming that a complete switch is shown therein; and

Fig. 3 is an enlarged perspective view of one of the improved terminalpin and contact element assemblies of the present invention.

Referring now more specifically to the drawings, therein is shown amercury contact switch 10 embodying the present invention and which isof the general type disclosed in detail in Burton Patent No. 2,459,306or Pollard, Patent No. 2,732,459. As indicated therein, the switch 10includes a glass enevlope 12in the lower end of which is sealed a commonterminal pin 14 comprising a hollow header which isused during thefabrication of the switch 10 for evacuating the envelope 12 and forintroducing both mercury and hydrogen gas under pres-' transversely fromeach other (Fig. 1) to provide a gap in which is disposed the upperportion 16a of the armature assembly 16. In accordance with the presentinvention, a tapered contact element 26 is secured to a lower portion ofeach of the terminal pins 18, 20, 22 and 24 in a position in which it isadapted to be engaged by the upper portion 16a of the armature assembly16. The armature 16 normally engages the contact elements 26 carried onthe terminal pins 18 and 2t} and is adapted to move out of engagementwith these contact elements and into engagement with the contactelements carired on the terminal pins 22 and 24 in response to theapplication of an operating signal to a coil having a centrally disposedopening in which the switch assembly is disposed.

Referring now more specifically to the contact elements 26, theseelements preferably are formed from hard drawn platinum and are somewhattrapezoidal in cross section. The inner wall surface of the elements 26are somewhat concave to conform to the outer surface of the terminalpins 18, 20, 22 and 24 thereby to facilitate the formation of a goodbond between the terminal pins and the elements 26, preferably bywelding. The elements 26 are secured to the terminal pins so that thelongitudinal axis of each of these elements is generally parallel to theaxes of the terminal pins.

In order to prevent the accumulation of globules of mercury in thefillets at the intersecting surfaces of the terminal pins 18, 20, 22 and24 and the contact elements 26, each of these elements is formed with abeveled, tapered or inclined lower end surface 26a which extendsgenerally inwardly and upwardly toward the upper end portion 16a of thearmature 16 so as to intersect a plane normal to the body of the element26 at an angle of 45 or less. Similarly, the upper end of each of theelements is formed with a tapered or beveled upper end surface 2612which extends downwardly and inwardly toward the upper end portion 16aof the armature assembly 16 so as to intersect a plane normal to theelement 26 at an angle of 45 or less. The use of this angle ofintersection between a plane normal to the element 26 and the planesdefined by the end surfaces 26a and 26b is particularly desirablebecause it has been experimentally determined that this inclination ofthe end surfaces 26a and 26b is adequate to prevent the formation oftheglobules of mercury which give rise to the bridging or avalancheeffect. The use of this degree of inclination also provides an adequatelength of inner end surface 26c for maintaining satisfactory contactwith the upper end portion 16a of the armature assembly 16 withoutunduly increasing the overall length of the contact element 26 with theattendant increase in the cost of the elements 26 due to the increasedamount of platinum necessary to form these contacts.

When the switch 10 is placed in an operating coil and the coil issupplied with operating signals, a varying magnetic field is producedwhich repeatedly oscillates the armature assembly 16 between theposition illustrated in Fig. 1 and one in which the upper end portion16a engages the terminal elements 26 carried on the make pins 22 and 24.Incident to this oscillation of the armature 16, the mercury provided inthe upper end portion 16a by capil lary action is transferred to theterminal pins 18, 20, 22 and 24 and to the contact elements 26 carriedthereon to provide wetted contacts of low resistance. However, thistransferred mercury has a tendency to form globules on the adjacentsurfaces of the pins 18, 20, 22 and 24. and on the contact elements 26.

The provision of the inclined end surfaces 26a and 26b on the elements26 prevents the accumulation of sufficiently large amounts of mercury onthe terminal pins 18, 20, 22 and 24 and the contact elements 26,particularly in the fillets between the contact elements 26 and theterminal pins, to bridge the contact elements 26 on the break pins 18and 20 and the make pins 22 and 24. The inclined end surfaces 26a and26b provide means by which the excess mercury from the terminal pins andthe contact elements 26 is returned under the force of gravity to thelower portion of the cavity defined by the sealed glass envelope 12. Bythus preventing the creation of the avalanche effect, the malfunctioningof the mercury contact switches 10 at high speeds is obviated, and theirreliability in high speed applications, such as in computing apparatus,is materially improved.

Although the present invention has been described in conjunction with asingle illustrative embodiment thereof, it should be understood thatmany other modifications can be made by those skilled in the art whichwill fall within the spirit and scope of the principles of thisinvention.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:

1. In a relay including a sealed envelope containing mercury and acapillary type armature movable at high speeds relative to a pluralityof contact supporting means, contact elements secured to said supportingmeans and adapted to be engaged by said armature, said elements eachcomprising a length of electrically conductive ma terial having a longerwall surface secured to one of said supporting means and a shorter Wallsurface spaced from said one supporting means and adapted to be engagedby said armature, said longer and shorter walls being connected by twoopposite end walls that are inclined respectively upwardly anddownwardly toward said armature.

2. In a relay including a vertically extending sealed envelopecontaining mercury and an upwardly extending capillary type armature, aplurality of spaced terminal pins sealed in said envelope and extendingdownwardly within said envelope, said armature being movable relative tosaid terminal pins at high speeds, and an elongated contact elementsecured to each of said pins adapted to be engaged by the upper end ofsaid armature, each of said elements extending generally along the axisof the terminal pin and having both an upper and generally flat endsurface inclined downwardly and inwardly toward the upper end of saidarmature and a lower and generally flat end surface inclined upwardlyand inwardly toward the upper end of said armature.

3. The relay set forth in claim 2 in which both of the inclined endsurfaces of each of said contact elements intersect a horizontal planeat an angle of 45 or less.

4. A contact element for use with wetted contact relays operable at highspeeds comprising an elongated length of electrically conductivematerial having longitudinally spaced and generally flat end surfaceswhich are inclined inwardly toward a plane passing transversely throughthe material to intersect the plane at an angle of 45 or less.

References Cited in the file of this patent UNITED STATES PATENTS

